Touch panels or touch screens are present in many different types of common modern electronic devices, such as cellular telephones, tablet computers, portable music and video devices, personal digital assistants, portable gaming devices, and so on. In these electronic devices the touch screen is part of the user interface of the device. The touch screen typically includes a display, touch sensors, and a touch controller. The touch sensors are typically some sort of transparent sensor array, such as an ultrasonic, resistive, vibration, or capacitive sensor array, that is attached to or formed as an integral part of the display. When a user touches the sensor array either with a finger or a stylus, the sensor array generates corresponding electronic sensor signals that are provided to the touch controller. From these sensor signals, the touch controller detects the occurrence of a touch or touch point P(X,Y). The touch controller also determines the type of “touch event” to be associated with the touch point P(X,Y), along with various characteristics of the touch event, and provides this information to processing circuitry in the electronic device. The processing circuitry operates in response to this information to allow a user to control the electronic device through these touches or touch points P(X,Y) on the touch screen.
The touch controller captures frame data from the touch sensors and processes this frame data to detect the presence of a touch point P(X,Y) and the type of touch event (i.e., touch-in event, touch-out event, touch-motion event) associated with the touch point. This processing is typically referred to as touch frame processing and through this processing the touch controller generates touch information including the type of touch event and the location of the touch event on the touch screen. The touch controller must reliably detect the presence of touch points P(X,Y) from the frame data. The detection of false touches in a touch screen occurs where the frame data from the touch sensors indicates a touch point P(X,Y) has occurred at a corresponding location on the touch screen when in fact no such touch point did in fact occur at that location, as will now be described in more detail below.
A typical capacitive touch sensor is formed by an array of conductive force lines Ci and sense lines Lj that are arranged in orthogonal to one another to form a matrix or array of touch or sensor nodes CiLj. The force lines Ci may be viewed as column lines and the sense lines Lj as row lines, where the array includes “i” force lines and “j” sense lines. The sensor nodes collectively detect the touch information, which includes location information (i.e., which sensor nodes indicate the presence of touch point), the touch event type, along with other parameters like pressure, size, and so on, as will be appreciated by those skilled in the art. The sensor nodes CiLj detect the touch information through variations of four “fringing” capacitances associated with each sensor node Ci,Lj.
Unfortunately, most capacitive touch screens are prone to unwanted capacitive changes in the sensor nodes CiLj even when there is no touch point P(X,Y) being applied. These unwanted capacitive changes may be detected by the touch controller as false touches. For example, when a sensor node CiLj associated with a given sense line Lj (i.e., in a given row of the sensor node array) is touched by a touch point P(X,Y), such a “touch” is a “true” touch and is detected as such in the form of the associated capacitance of the node exceeding an associated touch threshold. In this situation, however, the capacitances of the other sensor nodes Ci,Lj of the same sense line Lj also change, even without a touching or a touch point having actually occurred at the locations of these other sensor nodes. This is true because the single sensor node Ci,Lj at which a “true” touch point P(X,Y) has occurred affects its neighboring sensor nodes as well as the whole sense line Lj with a similar pattern of incremented or decremented capacitance values. If the capacitance values of these other sensor nodes CiLj that are part of the same sense line Lj cross the touch threshold, then the frame data associated with these other sensor nodes, when processed, may indicate that false touches have occurred at these other sensor nodes as well.
There is accordingly a need for improved circuits, systems, and methods of eliminating or reducing the detection of false touches in a touch screen.